Bidirectional unicable switching system

ABSTRACT

A two-way cable television broadcasting system wherein a single coaxial cable is used to deliver TV and FM programs to many subscribers with each subscriber having a specific allocated band of frequencies for reception of any desired television or FM program and where each subscriber can independently select the program desired to be seen and/or heard which will be delivered to the subscriber over an allocated band of frequencies. The subscriber drops from said coaxial cable are so arranged that they descend in frequency along the length of the feeder cable. Automatic switching of any incoming program to any drop is achieved by means of converting all incoming channels to a common I.F. frequency at an amplifier or control station and then deconverting said frequency to the desired outgoing band of frequencies.

This .[.application.]. .Iadd.reissue is a continuation of Ser. No.116,192, filed Jan. 28, 1980, now abandoned, which is reissue of U.S.Pat. No. 4,077,066, issued Feb. 28, 1978, based on application 672,066,filed Mar. 30, 1976, which .Iaddend.is a continuation-in-part of Ser.No. 558,425, filed Mar. 14, 1975, now abandoned; which is a continuationof Ser. No. 405,846, filed Oct. 12, 1973, now abandoned.

.Iadd.SUMMARY OF THE INVENTION .Iaddend.

This invention relates to a two-way coaxial sending and receiving systemwherein a single coaxial cable is used to send and receive televisionsignals with each subscriber drop being assigned its own specificallocated band of frequencies.

It is well known in the art that cable television systems today have thecapabilities of delivering up to 35 different television channels ofprogramming plus the full spectrum of FM services to all subscribers.Existing systems are "party line" type systems whereby the sameprogramming is delivered to all subscribers. These cable systems alsohave the capability of returning television signals to the headend.

There have been other types of systems proposed in the past whereby eachsubscriber has separate downstream and upstream cables therebypermitting him to remotely select any available program. The subscribercould dial the desired program and at a local switching center, thesubscriber's cable would be interconnected to that channel. This type ofswitching system presents the possibility of a subscriber being able torequest television programs from libraries of video tapes providingeducational programs, foreign language lessons, cultural or sportingevents. This system had one inherent weakness: the requirement for aseparate feeder cable to every subscriber. This requires the use, ineither aerial or underground construction, of large bundles of cables.This type of system--in spite of its promise--has not succeeded in thiscountry, because of excessive costs.

.Iadd.OBJECTS OF THE INVENTION .Iaddend.

It is the general object of this invention to provide the above notedservices by using a system wherein a single coaxial cable is used todeliver television programs to many subscribers, where each subscriberhas a specifically allocated television channel or band of frequenciesfor reception of desired programs, where each subscriber independentlyselects the program to be sent on the subscriber's assigned channel,where all subscribers can receive FM signals, and where a descendingorder of television frequencies is delivered to subscribers on thefeeder cable. The same feeder coaxial cable that is used for receptionof the signal is used to transmit back to the amplifier or controlstation a signal from the subscriber to select the desired program.

A still further general object of this invention is the use of this samefeeder coaxial cable to send back to the control station a televisionsignal on the assigned channel. This program can be used for two-waytelevision of broadcast quality between any two subscribers or for aconference of subscribers.

This invention is similar in concept to the prior art "WiredBroadcasting Systems" shown by Eric J. .[.Gargine.]..Iadd.Gargini.Iaddend., U.S. Pat. No. 3,665,331 and Ralph PortonGabriel, U.S. Pat. No. 3,801,735. A major difference in this system fromthe above systems is that rather than providing two separate feedercables to each subscriber (one downstream, the other upstream), up to 35subscribers can utilize the same feeder cable for receiving signalsdownstream and sending them upstream. Each subscriber on a given feedercoaxial cable is allocated a separate channel for reception andtransmission of programs plus the transmission of control signals. Thesechannels are allocated to individual subscribers on the basis ofdistance along the feeder from the control station with the closersubscribers being assigned a higher frequency spectrum.

The primary advantage of this system along with the other switching typewired broadcasting systems is that each subscriber has the capability ofremotely selecting one of possibly hundreds of available television orother programs at any time. The immediate applications using existingsingle trunk cable systems is primarily one-way, downstream where thesubscribers choice is limited to 35 television channels and fullspectrum of FM as this is the total delivered to each control stationand therefore the total available for connection to the subscribers whorequested them. Later there can be additional origination of programmingat the control station (which could be located in a public school orlibrary). To further increase the subscriber's program choices the cableoperator can duplicate the trunk part of the system. Other possibleapplications, where the trunk part of the system is two-way, are for thesubscriber's return signals to be sent to other parts of the system uponbeing received at the control station.

It is still a further object of this invention to apply it to multi orsingle dwellings. Since both the downstream and upstream services usethe same bandwidth for each subscriber and since this bandwidth is wideenough to a television channel, it is possible for one or any number ofsubscribers to simultaneously originate television programming. Thisprogramming can be automatically routed back to the control station ontoan upstream trunk line to the headend, and then downstream to anotherpreselected subscriber.

It is a still further object of the instant invention that it isdistinguished from present CATV systems in the following manner:

CATV systems generally have up to two line extender amplifiers cascadedin the feeders from each output of the bridger amplifier; the proposedsystem eliminates these line extenders. The limiting factor for distanceof subscriber service from a feeder, in a CATV system, is the.[.attention.]. .Iadd.attenuation .Iaddend.of the coaxial cable at thetop frequency for which the system is designed. The instant inventionextends feeders more than twice as far without amplification as itslimiting factor is the attenuation of the coaxial cable at channel 2.This feature provides reduced system cost and elimination of systemdistortions as introduced in the line extenders. The feeder is a coaxialcable whose size (and therefore attenuation) is determined by thedistance to the furthest subscriber. Several feeder cables can beparalleled for areas of high density of homes.

The above mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will best be understood by reference to the following descriptionof embodiments of the invention taken in conjunction with theaccompanying drawing the description of which follows:

.Iadd.BRIEF DESCRIPTION OF THE DRAWINGS .Iaddend.

FIG. 1 is a diagrammatic representation of the Trunk, Bridger andControl Station and feeder cable of the instant invention which issimilar to a conventional CATV system such as that shown in "Two-wayApplications for Cable Television Systems in the 70's." (Ronald K.Jurgen, Spectrum of IEEE, November 1971, FIG. 4, page 45.) A significantdifference however is the elimination of line extender and themodifications to the Trunk and Bridger Station to include a ControlStation.

FIG. 2 is a diagrammatic representation of a typical feeder cableshowing the Control Station terminal and the coaxial cable disclosingsubscriber drops along its effective length.

FIG. 3 is a diagrammatic representation from the Control Station showingthe downstream paths of the television signals to the individualsubscribers.

FIG. 4 is a diagrammatic representation of the Control Station showingthe downstream, upstream and control signal paths.

FIG. 5 is a diagrammatic representation of a section of the ControlStation that processes the subscriber's control signal.

FIG. 6 is a diagrammatic representation of a two-way subscriber dropfrom the feeder cable to the receiver and back.

In present CATV systems, at some trunk locations, some of the broadbandTV and FM signal is split off with a directional coupler, amplified in abridger amplifier and distributed down feeder lines which pass thevarious subscriber locations. For those wishing to subscribe, a tap ismade into the feeder cable and to a cable drop to the subscriber'sresidence, which drop is connected to the subscriber's TV set. Allchannels are on the cable and are received by all subscribers.

This system incorporates separating into individual channels thecombined signals at the control Station, converting them to common I.F.frequencies and switching each one to the desired outgoing R.F. channeland feeder cable to satisfy the request of a subscriber. The switchingcircuitry can be of any type capable of being controlled by a remotevoltage. Therefore, by the application of a frequency selective voltage,any subscriber can have any channel connected to his/her feeder cable.

As by way of example the frequency allocation to each feeder can be asfollows:

    ______________________________________                                        SUBSCRIBER FREQUENCY ALLOCATIONS                                              Subscriber No.  MHz                                                           ______________________________________                                        1               294-300                                                       2               288-294                                                       3               282-288                                                       4               276-282                                                       5               270-276                                                       6               264-270                                                       7               258-264                                                       8               252-258                                                       9               246-252                                                       10              240-246                                                       11              234-240                                                       12              228-234                                                       13              222-228                                                       14              216-222                                                       15              210-216                                                       16              204-210                                                       17              198-204                                                       18              192-198                                                       19              186-192                                                       20              180-186                                                       21              174-180                                                       22              168-174                                                       23              162-168                                                       24              156-162                                                       25              150-156                                                       26              144-150                                                       27              138-144                                                       28              132-138                                                       29              126-132                                                       30              120-126                                                       31              82-88                                                         32              76-82                                                         33              70-76                                                         34              64-70                                                         35              58-64                                                         ______________________________________                                         Note:-                                                                        88-108 MHz is used for F.M. signals to all subscribers.                       108-120 MHz is not used as it includes aircraft navigation band  even         though there should be no radiation problem.                             

.Iadd.DETAILED DESCRIPTION OF THE DRAWINGS .Iaddend.

In the following detailed description and the drawing, like referencecharacters indicate like parts.

In FIG. 1 is shown a Trunk and Bridger Amplifier and Control Stationwhere the Control Station 1 receives signals from the bridger amplifier2 and sends them to the subscribers. It also receives signals fromsubscribers and sends them upstream to the cable system headend by wayof the Return Trunk Amplifier 3.

In FIG. 2 is shown a Control Station 1 and a feeder cable 10, descendingfrom said Control Station. The closest subscriber 4 is allocated the TVchannel spectrum of 294-300 MHz plus the FM spectrum 88-108 MHz and themost distant subscriber 5 is allocated the TV channel spectrum 54-60 MHzplus the FM spectrum of 88-108 MHz. The other subscribers on the feedercable are assigned TV channel spectrums in a descending order plus theFM spectrum 88-108 MHz.

In FIG. 3 is shown the downstream functions of the Control Station 1, toone of the feeder cables, which receives the multichannel output of thebridger amplifier 2 through directional couplers 6 and processes each TVchannel separately, through the down converters 7 that provides a commonI.F. band of frequencies 41 to 47 MHz. The outputs of these convertersare connected with further directional couplers 6 to the input terminalsof switching network 8. The output of the switching network connects therequested channel's I.F. to TV channel up-converter 9. This switchingcan be mechanical, electronic or any automatic type where a desiredprogram can be sent to the proper channel converter through additionaldirectional couplers 6 to feeder cable 10. Local TV program originationwhether live or by tape is handled the same way. This is shown byvideotape player 11 connected to modulator 12 for conversion of video toI.F. and is available to be switched to any subscriber. By this systemthe Control Station connects any desired I.F. modulation to any outputchannel on any feeder.

The FM signals are handled differently in that the broadband spectrum88-108 MHz is maintained throughout; further directional couplers 6connect the bridger amplifier's output to FM amplifier 13 and thevarious feeder coaxial cables 10. By this system the Control Stationconnects FM to all feeder cables.

In FIG. 4 is shown the downstream, upstream and control functions of theControl Station 1. The downstream functions are the same as shown inFIG. 3 with signals from bridger amplifier 2 being connected viadirectional coupler 6, being converted to I.F. by down-converter 7,being switched by 8 to the desired channel up-converter 9 and connectedto the feeder cable 10 through a channel bandpass filter 14.

The upstream television signals from feeder cable 10 are fed throughdirectional coupler 6, through the channel bandpass filter 14, throughother directional couplers to an I.F. down-converter 7, then through theautomatic switch network 8 to the desired channel up-converter 9 andthrough a directional coupler to the return trunk amplifier 3, in theTrunk and Bridger Amplifier and Control Station. These functions enablethe TV or data return channels to be ultimately fed to the Cable Systemheadend, there to be redistributed to any other subscriber.

The upstream control signals are fed to the frequency selective voltagecontrol network 15 where they provide frequency selective voltages tocontrol the automatic switching of both upstream and downstream signals.For a detailed description of this network see FIG. 5.

In FIG. 5 is shown various functions that are employed in controllingthe switching network that allocates the television channels being sentand received by a subscriber. This is done by a network that receivesand responds to a control signal from a subscriber. A subscriber cansend this signal by modulating with a discrete frequency the lower R.F.band edge of the subscriber's allocated channel. All taps, cable,filters and accessories on the feeder cable 10 are two-way so thiscontrol signal is split off the feeder at the Control Station by adirectional coupler 6, connected to channel R.F. bandpass filter 14, toan R.F. detector 16, then a low frequency bandpass filter 17 thataccepts the desired frequency selective signal and feeds it toamplifiers and that develops a control voltage for the automaticswitching. Items 16, 17 and 18 are components of the frequency selectivecontrol network 15 in FIG. 4. Items 6, directional couplers, which arein the control path after 14 are not shown on this FIG. 6.

The conversion of any incoming television channel at the ControlStations to an outgoing television channel is accomplished by convertingall incoming channels to a common I.F. frequency, switching them bymeans of control signals and then reconverting them to the desiredoutgoing frequency.

The switching, which is not shown, can be typical of any of those thatare employed in two-way cable television systems such as that shown atthe program exchange in U.S. Pat. No. 3,801,705 of Gabriel, referred toabove, for non-duplication or other services. It can be electronic,mechanical or any automatic type wherein the control signal from anysubscriber will actuate the switching circuit and cause the desiredprogram to be sent to the subscriber.

In FIG. 6 is shown a two-way subscriber drop which includes the two-wayfeeder cable 10, directional coupler 28 and an FM bandpass filter 19 topass FM to the subscriber irrespective of TV channel allocation. Thefeedthru section of the FM filter connects all TV signals to a TVchannel bandpass filter 14, to the subscriber's two-way interfaceterminal 20 and to the TV receiver 21.

The upstream TV transmitting circuit can comprise of a TV camera 22,microphone 23 and modulator 24. An upstream control signal transmittingcircuit could include a lower band edge R.F. oscillator 25, a discretelow frequency oscillator 26 and a mixer or modulator 27. This controlsignal can be switched on by the subscriber's interface terminal 20.

While the principles of the invention have been described in connectionwith specific apparatus, it is to be clearly understood that thisdescription is made only by way of example and not as a limitation tothe scope of the invention.

I claim:
 1. In a cable distribution system having a head end, means atsaid .[.heat.]. .Iadd.head .Iaddend.end for receiving multipletelevision channels, a coaxial cable having multiple channel capacityconnected to said head end, a bridger amplifier connected to the coaxialcable for receiving and amplifying signals in the multiple televisionchannels, a control station connected to the bridger amplifier, saidcontrol station including a switching network and channel convertersconnected to the bridger amplifier, a feeder cable having a plurality ofsubscriber allocated channels, said feeder cable connected to theswitching network and channel converters, a plurality of subscriberdrops connected to the feeder cable, each subscriber drop beingconnected to a single subscriber allocated channel in the feeder cable,thereby allocating one channel in the feeder cable to each subscriberdrop, means at each subscriber drop for sending a control signal to thecontrol station on the subscriber allocated channel allocated to thatsubscriber drop to control the switching network at the control station.2. In a system set forth in claim 1, wherein means are located at thesubscriber drop for sending a television signal to the control stationon the same subscriber allocated television channel allocated to thesubscriber drop and means at said control station for sending thetelevision signal to other subscribers.
 3. In a system as set forth inclaim 1, wherein the allocated channel frequencies are allocated tosubscriber drops in a descending order depending on the distance of suchsubscriber drop from the control station.
 4. In a system as set forth inclaim 1 wherein means for sending the control signal from a subscriberdrop to the control station comprises means for sending the controlsignal on the lower end of the subscriber drops' allocated.[.frequency.]. .Iadd.frequencies.Iaddend..
 5. The cable distributionsystem of claim 1 wherein the control station switching network andchannel converters comprise a first plurality of channel convertersconnected to bridger amplifier for converting multiple channels from thecoaxial cable to a common I.F. band of frequencies, a switching networkconnected to the first converters, and a second plurality of convertersconnected to the switching network and to the feeder cable forconverting the common I.F. band of frequencies to the separatesubscriber allocated channel. .Iadd.6. In a system as set forth in claim1, wherein the switching network switches programs to any or allsubscribers on request. .Iaddend. .Iadd.7. In a cable distributionsystem having a head end, means at said head end for receiving multiplechannels, a coaxial cable having multiple channel capacity connected tosaid head end, a bridger amplifier connected to the coaxial cable forreceiving and amplifying signals in the multiple channels, a controlstation connected to the bridger amplifier, said control stationincluding a switching network and channel converters connected to thebridger amplifier, a feeder cable having a plurality of subscriberallocated channels, said feeder cable connected to the switching networkand channel converters, a plurality of subscriber drops connected to thefeeder cable, each subscriber drop being connected to a singlesubscriber allocated channel in the feeder cable, thereby allocating onechannel in the feeder cable to each subscriber drop, means at eachsubscriber drop for sending a control signal to the control station onthe subscriber allocated channel allocated to that subscriber drop tocontrol the switching network at the control station. .Iaddend. .Iadd.8.In a system set forth in claim 7, wherein the allocated channelfrequencies are allocated to subscriber drops in a descending orderdepending on the distance of such subscriber drop from the controlstation. .Iaddend. .Iadd.9. In a system as set forth in claim 7, whereinthe switching network controls programs from multiple channel sourcessuch a libraries and schools which are sent to each subscriber on hisallocated channel for reception of desired programs. .Iaddend..Iadd. 10.The cable distribution system of claim 7, wherein the control stationswitching network and channel converters comprise a first plurality ofchannel converters connected to a bridger amplifier for convertingmultiple channels from the coaxial cable to a common I.F. band offrequencies, a switching network connected to the first converters, anda second plurality of converters connected to the switching network andto the feeder cable for converting the common I.F. band of frequenciesto the separate subscriber allocated channel. .Iaddend. .Iadd.11. In asystem set forth in claim 7, wherein means are located at the subscriberdrop for sending a signal to the control station on the same subscriberallocated channel allocated to the subscriber drop and means at saidcontrol station for sending the signal to other subscribers. .Iadd. 12.A cable distribution system having a head end, means at said head endfor receiving multiple bands of frequencies, a coaxial cable havingcapacity for multiple bands of frequencies connected to said head end, abridger amplifier connected to the coaxial cable for receiving andamplifying signals in the multiple bands of frequencies, a controlstation connected to the bridger amplifier, said control stationincluding a switching network and frequency converters connected to thebridger amplifier, a feeder cable having a plurality of subscriberallocated bands of frequencies, said feeder cable connected to theswitching network and frequency converters, a plurality of subscriberdrops connected to the feeder cable, each subscriber drop beingconnected to a single subscriber allocated band of frequencies in thefeeder cable, thereby allocating one band of frequencies in the feedercable to each subscriber drop, means at each subscriber drop for sendinga control signal to the control station on the subscriber allocated bandof frequencies allocated to that subscriber drop to control theswitching network at the control station. .Iaddend. .Iadd.
 13. A systemset forth in claim 12 wherein means are located at the subscriber dropfor sending a signal to the control station on the same subscriberallocated band of frequencies allocated to the subscriber drop and meansat said control station for sending the signal to other subscribers..Iaddend..Iadd.
 14. A system as set forth in claim 12, wherein theallocated bands of frequencies are allocated to subscriber drops in adescending order depending on the distance of such subscriber drop fromthe control station. .Iaddend..Iadd.
 15. A system as set forth in claim12, wherein means for sending the control signal from a subscriber dropto the control station comprises means for sending the control signal onthe lower end of the subscriber drops' allocated band of frequencies..Iaddend..Iadd.
 16. A system as set forth in claim 12, wherein thecontrol station switching network and frequency converters comprise afirst plurality of frequency converters connected to bridger amplifierfor converting multiple bands of frequencies from the coaxial cable to acommon I.F. band of frequencies, a switching network connected to thefirst converters, and a second plurality of converters connected to theswitching network and to the feeder cable for converting the common I.F.band of frequencies to the separate subscriber allocated band offrequencies. .Iaddend.